It was not a secret in USSR that Germans participated in early post-war rocketry works. Boris Chertok - in post-Soviet memoirs - describes works of team of Herman Grottrup. I'm not sure von Ardenne had that much influence on space-related technologies. Soviets rather have hidden their own projects, trying to paint too rosy a picture of a string of successes.
Orbit-capable rockets were for a long time being developed for military goals, it was only governments which can afford them and governments had their own justifications. In USA, for example, a lot of military rocket technologies found their way into civilian NASA programs.
In post-Soviet memoirs, indeed. Of course Chertok would know who worked there. The general populace only heard rumours that possibly Guderian was teaching in a military academy and was convinced that of course Tu-4, Elbrus, the Bomb, rockets, AK-47 and all that were purely homegrown inventions.
At least after Stalin's death they stopped claiming that pretty much everything has been invented or discovered by Russians (with an occasional Ukrainian or Uzbek thrown in for good measure).
Orbit-capable rockets were for a long time being developed for military goals, it was only governments which can afford them and governments had their own justifications. In USA, for example, a lot of military rocket technologies found their way into civilian NASA programs.